Problem: In geometry class, the girl to boy ratio is $6$ to $10$. If there are $30$ girls, how many boys are there?
A ratio of $6$ girls to $10$ boys means that there is a group of $6$ girls for every group of $10$ boys. If there are $30$ girls, then there are $5$ groups of $6$ girls each. Because we know the ratio is $6:10$ , there must be $5$ groups of $10$ boys each. There is a total of $50$ boys in geometry class.